import collections,sys,math,functools,operator,itertools,bisect,heapq,decimal,string,time,random
#sys.setrecursionlimit(10**9)
#sys.set_int_max_str_digits(0)
#input = sys.stdin.readline
n = int(input())
se = [set() for i in range(n)]
for i in range(n):
    check = [0 for j in range(26)]
    s = input().rstrip()
    for j in s:
        check[ord(j) - ord('a')] += 1
    for j in range(26):
        check[j] += 1
        se[i].add(tuple(check))
        check[j] -= 1

for i in range(n):
    for j in se[i]:
        cnt = 0
        for k in range(n):
            if k == i:
                continue
            if j in se[k]:
                cnt += 1
        if cnt == 0:
            for k in range(26):
                for l in range(j[k]):
                    print(chr(ord('a') + k),end='')
            print()
            exit()
print(-1)